Visible lamp including selenium or sulfur

ABSTRACT

A lamp for providing visible light which utilizes a fill containing selenium and/or sulfur, or compounds of these substances. The lamp is excited such that the excited fill emits radiation from elemental selenium and/or elemental sulfur which is in a continuous band principally within the visible range.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of Application Ser. No.08/071,027, Jun. 3, 1993 now U.S. Pat No. 5,404,076, which is acontinuation of application Ser. No. 07/604,487, now abandoned, filedOct. 25, 1990.

BACKGROUND OF THE INVENTION

The present invention is directed to a new, high power lamp.

High power lamps are used for many illumination applications. Theincandescent and fluorescent lamps, so familiar in homes and offices, donot provide enough illumination for many commercial and industrialapplications. In fact, the lamp which has gained acceptance and which istypically used for high power illumination is known as the highintensity discharge (HID) lamp. This lamp is simple in structure, andgenerally consists of a glass envelope which contains two electrodes anda fill which vaporizes and becomes a gas when the lamp is operated.

The fill in the HID lamp usually contains mercury as its primarycomponent. However, this is undesirable because mercury is a highlytoxic and environmentally hazardous substance. Thus, if a HID lampshould break, dangerous mercury fumes would be emitted, and after theuseful life of the lamp is over, there is no easy way to safely disposeof the mercury containing envelope. The widespread use of mercurycontaining lamps has been recognized as a serious environmental problem.

It is a feature of the present invention that instead of mercury, asubstance which contains sulfur or selenium is used in the lamp fill.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, theelemental sulfur or selenium, or compounds of these elements, isincluded in a lamp fill. The fill is present at a pressure of at leastabout 1 atmosphere, and is excited with electromagnetic energy at arelatively high power density. Each of the above-mentioned substanceshas a low vapor pressure at room temperature, yet a high vapor pressureat typical lamp operating temperatures. The preferred embodiment of theinvention utilizes a sulfur fill.

In accordance with a further aspect of the invention, elemental sulfuror selenium, or compounds of these elements is used as the primaryradiating component of a lamp fill. The term "primary radiatingcomponent" as used herein means that radiating component of the fillwhich is present at at least about the same or greater partial pressurethan the other radiating fill components during operation of the lamp,or that radiating component which is the sole radiating component in thefill.

There are many ways to measure how good a lamp is, and amongst thoseskilled in the lamp art the use of various standardized performanceindicators has arisen. These include the luminous efficacy of the lamp,its rated life, lumen maintenance, chromaticity, and color renderingindex (CRI). Finally, the stability of the color of the light which isemitted by the lamp is important, as this may change over time. Thecloser these accepted indicators are to ideal, the better theperformance of the lamp.

As described above, the lamp of the invention avoids the environmentalhazards which are associated with mercury based lamps, and additionallythe resultant performance indicators for the lamp are relatively good.

In a first embodiment of the invention, a high power lamp of theelectrodeless type is provided, which is powered by microwave energy.High power electrodeless lamps are well known in the art, but haveinevitably if not always contained a mercury fill. Additionally, thelamps have primarily been used for their output in the ultravioletrather than the visible portion of the spectrum. In the electrodelesslamp of the invention, a high pressure fill at least as high as 1atmosphere is utilized, which includes sulfur or selenium, or a compoundthereof. Additionally, the fill may include a gas such as argon orxenon. The high pressure fill is excited at power densities in excess of50 watts/cc, and preferably in excess of 100 watts/cc. Furthermore,various additives such as metal halides, arsenic or Boron, may beincluded in the fill to emphasize different areas of the spectrum.

The efficiency of production of useful radiation of the lamp of theinvention is relatively high. In fact, it is significantly higher thanfor the conventional electrodeless lamp which utilizes a mercury fill.The ability to provide such a lamp is an unexpected result, as the fillsubstances used in accordance with the invention have a higher heatconductivity than mercury so that it would be expected that more heatwould be lost to the bulb walls, and that the efficiency of productionof useful radiation would be lower than with the mercury lamp.

In a further embodiment of the invention, an arc lamp which haselectrodes is provided. This is similar to the previously describedmercury containing HID lamp, but instead of mercury, the fill includes asulfur or selenium containing substance. As in the case of theelectrodeless lamp, the addition of additives to the fill may be used toemphasize particular spectral regions. For example, sodium might be usedto increase the orange and red radiation from the lamp.

In the prior art, low pressure, low power lamps are known which havebeen used in the laboratory for the scientific study of the spectrum(atomic spectroscopy). It is conventional in such laboratory to use eachof the elements of the periodic table, including the fill substancesproposed herein, as the fill for electrodeless and arc lamps, so as togenerate the atomic and molecular spectra of such elements. However,such lamps would be wholly unsuitable as high power visible,illumination sources. In fact, when the spectra generated with the lampsof the present invention were compared with the atomic or molecularspectrum generated by the low power, low pressure atomic spectroscopylamp using the same fill, it was noted that for at least someimplementations of the present invention, the ultraviolet part of thespectrum which appeared prominently in the spectrum of the atomicspectroscopy source was substantially and unexpectedly suppressed in thelamp of the invention, thus resulting in higher luminous efficacy, andin the generation of less harmful ultraviolet radiation.

It is thus an advantage of the present invention that a new, high powerlamp is provided which does not need to contain mercury.

It is a further advantage of the invention that a new, high power lampbulb is provided which does not need to contain mercury.

It is a further advantage of the invention that a new, high power lampis provided which has relatively good performance indicators.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better appreciated by referring to theaccompanying drawings, wherein:

FIG. 1 shows a first embodiment of the invention.

FIG. 2 shows a further embodiment of the invention.

FIG. 3 is a spectral plot for an electrodeless lamp utilizing a sulfurbulb fill.

FIG. 4 is a spectral plot for an electrodeless lamp utilizing a bulbfill containing sulfur and cadmium iodide.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, a first embodiment of the invention is depicted.Lamp 2 is an electrodeless lamp which is powered by microwave energy.Bulb 3, which contains a high pressure fill, and is made of quartz orother suitable material, is supported in a microwave cavity, which iscomprised of conductive housing 4 and mesh 5. Magnetron 6 generatesmicrowave energy, which is fed by waveguide 7, to coupling slot 8 of themicrowave cavity.

This excites the bulb fill to a plasma state, whereupon light is emittedby the fill, which is transmitted out of the cavity through mesh 5. Themesh is metallic, and is constructed so that it is substantially opaqueto microwave energy, while being substantially transparent to the lightwhich is emitted by bulb 3. The bulb is rotated by rotator 9, and thebulb envelope is cooled by gas which is fed in to plenum 10 and outthrough nozzles 11.

In accordance with an aspect of the invention, the fill in bulb 4includes elemental sulfur or selenium, or a compound of one of theseelements. In accordance with a further aspect of the invention, thissubstance is present as the primary radiating component of the bulbfill. It is further desirable to use a fill component which aids instarting the discharge, and for example, a small amount of an inert gas,such as argon or xenon may be used for this purpose.

The lamp which is shown in FIG. 1 may be characterized as a high power,high pressure lamp. Thus, the fill in bulb 3 is present in amounts suchthat the fill pressure is at least one atmosphere or above at operatingtemperature, and is preferably 2 to 20 atmospheres. Additionally, theamplitude of the microwave energy which is fed to the cavity is suchthat the power density of the energy which is coupled to the fill is atleast 50 watts/cc, and preferably in the range of 100 to 400 watts/cc.It should be understood that the absolute amount of the primary fillcomponent in solid form which is used in the bulb may vary depending onwhich substance is used, e.g., sulfur or selenium, but the amount alwayswill be such to produce the desired pressure range at operatingtemperature, i.e., the temperature of the bulb during normal operationat a power density of 50 watts/cc or greater. The fill pressure ismainly controlled by the primary fill component, which typically has asubstantially higher partial pressure than that of the inert gas whenthe lamp is operational. Further, the illumination provided by the lampshown in FIG. 1 may be augmented in various regions of the spectrum byincluding certain additives in the fill. By way of non-limitativeexamples such additives may include metal halides, arsenic, boron,carbon and bismuth. Examples of some of the many metal halides which canbe used are CdI₂, HgCl, and InI₃. Also, in certain implementations, theaddition of some mercury may improve operation by reducing the restriketime of the lamp.

As noted above, in addition to using sulfur, selenium, and phosphorousin elemental form, compounds of these elements may be used. For example,CS₂, InS, As₂ S₃, SeO₂ and SeCl₄ as well as other compounds of sulfurand selenium, may be used. The term "a sulfur containing substance" asused herein, includes both elemental sulfur and sulfur compounds, whilethe same is true for the corresponding terms as applied to selenium. Itshould be appreciated that the primary radiating component of the fillmay be comprised of a combination of a sulfur containing substance orsubstances and selenium containing substance, rather than only one ofthese substances. Additionally, the primary radiating component may becomprised of a mixture of the elemental form and a compound(s) of aparticular substance, e.g., sulfur.

While microwave energy is the preferred mode of excitation of lamp 2, itwould also be possible to provide excitation with electromagnetic energyin the radio frequency range. Since this typically would involvewrapping an excitation coil around the bulb, which would obscure some ofthe emitted light, the microwave mode of excitation is preferred.However, the term "electromagnetic energy" as used herein refers to bothmicrowave and r.f. modes. Also, while the microwave cavity which isillustrated in FIG. 1 does not include a reflector, a reflecting cavitycould also be used.

As mentioned above it appears that the performance indicators of thelamp of the invention are relatively good. In this regard it is notedthat electrodeless lamps, which have heretofore been used mainly toproduce ultraviolet as opposed to visible light, tend to maintain theirlumen output at a high level for a longer period of time than arc lamps,and this may be an advantageous property of the electrodeless lampembodiment of the present invention.

An additional advantage of the present lamp is that the primaryradiating fill component may be a single element. Thus, the most commontype of HID lamp presently used for high power illumination applicationsis the metal halide type HID lamp, wherein mercury is combined with thehalide of another metal or metals in order to achieve the desiredspectral output. A commonly used combination is Hg+ScI+NaI. The partialpressure of the additive metals is determined by the amount of metalhalide in the lamp and by the temperature of the coldest spot on thelamp. The result is that variations in these parameters due tomanufacturing tolerances or lamp aging will cause changes in the partialpressure of the additive, which in turn causes changes in the amount ofoutput and in the spectral distribution of the output. On the otherhand, since the present lamp may have only a single radiating fillcomponent, or in accordance with an aspect of the invention have a fillwhich consists essentially of a sulfur containing substance or, aselenium containing substance, and an inert gas, any effect caused bythe partial pressures of different fill components changing at differentrates will not occur.

A further advantage of the lamp of the invention is that it may emitprincipally molecular as opposed to atomic radiation which results in asmoother spectrum without peaks or abrupt transitions and possibly abetter color rendering index. In this regard it is noted that non-metalshave found little application as fill materials in the prior art, andone reason for this is that the primary atomic spectral lines of thenon-metals do not lie in the visible region. However, the presentinvention, at least in certain implementations relies on molecularradiation as the dominant source, and is able to provide radiationprincipally within the visible range. A unique feature of the lamp ofthe present invention may be that it is a high luminous efficacy lampwhich emits principally molecular radiation.

A still further advantage of the electrodeless lamp embodiment of theinvention is that it is a compact, high power, visible radiator. Thus,the diameter of the bulb is typically only 2-3 cm, while outputs ofabout 140 lumens/watt or greater are possible.

A further embodiment of the invention is shown in FIG. 2. This is an arclamp 20 which is comprised of quartz envelope 22 having electrodes 24and 26, and containing fill 28. To excite the fill, an A.C. voltage isimpressed across the electrodes, whereupon an arc discharge occurstherebetween

In accordance with the invention, the fill in envelope 22 includes asulfur containing substance or a selenium containing substance. Inaccordance with an aspect of the invention, this fill substance is theprimary radiating component in the fill. The substance may be elementsulfur or selenium, or compounds or these elements. Additionally, asmall amount of an additional gas to aid in starting is provided, whichcan be an inert gas, such as argon or xenon.

As in the case of the electrodeless lamp, the fill is present at a highpressure of at least about 1 atmosphere and preferably in the range ofabout 2-20 atmospheres. This pressure is controlled mainly by thesulfur, or selenium containing substance, the partial pressure of whichis at least about 1 atmosphere. Additionally, an electrical voltage isapplied across the electrodes such that a power density of at least 60watts/cm, exists. The electrodes 22 and 24 are made of or plated with aspecial material, such as platinum, to prevent chemical reactions withthe fill gas, which may lead to electrode deterioration. Electrodematerials other than platinum, which do not react with the fill gas, maybe used.

In one implementation of the invention, the fill of either anelectrodeless or arc lamp is arranged so that sulfur or seleniumcontaining substance, is the sole radiating component in the bulb fill.In such an implementation, the sulfur, selenium, or phosphorous, orcompound, may be the only substance in the fill except for a smallamount of a gas to aid starting, e.g., argon or xenon.

As a specific example of the invention, an electrodeless quartz bulb ofspherical shape having an internal diameter of 2.84 cm was filled with0.062 mg-moles/cc of sulfur, and 60 torr of argon. When the bulb wasplaced in a microwave cavity and excited with microwave energy at apower density of about 280 watts/cc, visible light was emitted having aspectrum as shown in FIG. 3. The luminous efficiency of the lamp wasabout 140 lumens/watt. Additionally, it is noted from the spectrum thatthere is minimal UV radiation beneath 350 nm. This feature helps toincrease the luminous efficacy of the lamp and also enhances the safetyof the lamp, as UV radiation is a health hazard. It is also noted fromFIG. 3 that the spectral plot is smooth and does not contain sharppeaks, which results from the fact that the lamp is principally amolecular as opposed to an atomic radiator.

As a further specific example of the invention, an electrodeless bulb ofspherical shape having an internal diameter of 2.84 cm was filled with0.053 mg-moles/cc of sulfur, 0.008 mg-moles/cc of cadmium and 0.003mg-moles/cc of cadmium iodide. When the lamp was excited with microwaveenergy at a power density of 280 watts/cc, visible light was emittedhaving a spectrum as shown in FIG. 4. The luminous efficacy of the lampwas about 134 lumens/watt. Additionally, it is noted that the spectrumhas a shoulder at 580 nm, which is caused by the CdS and anothershoulder at 650 nm, which is caused by the CdT.

A new, high power lamp which can be made without mercury has thus beendisclosed. While the lamp has been described primarily as a high powervisible source of illumination, certain implementations may find use inother areas of the spectrum, e.g., the U.V. Additionally, while theinvention has been illustrated in accordance with specific embodiments,it should be understood that variations falling within the spirit of theinvention will occur to those skilled in the art, and the invention isto be limited only by the claims which are appended hereto andequivalents.

We claim:
 1. A lamp bulb for providing visible radiation, comprising,alight transmissive envelope, and a fill in said envelope includingelemental selenium in gaseous form which is obtained when said fill isexcited by sufficient power in operation, in an amount such that theexcited fill emits radiation from the elemental selenium withsubstantially all of the radiation from the elemental selenium beingemitted in a continuous band principally within the visible range. 2.The lamp bulb of claim 1 in combination with,means for exciting saidfill with sufficient power to cause said elemental selenium to emit saidradiation substantially all of which is emitted in a continuous bandprincipally within the visible range.
 3. The apparatus of claim 2wherein said means for exciting applies microwave or r.f. power to thefill.
 4. The apparatus of claim 3 wherein said bulb is electrodeless. 5.The apparatus of claim 2 wherein said elemental selenium emits morevisible radiation than any other component of the fill.
 6. The apparatusof claim 2 wherein the visible radiation which is emitted from theelemental selenium is molecular radiation.
 7. The apparatus of claim 2wherein the pressure of the fill during operation is at least about oneatmosphere.
 8. The apparatus of claim 7 wherein the fill pressure iscontrolled primarily by the elemental selenium.
 9. The apparatus ofclaim 8 wherein said means for exciting applies microwave or r.f. powerto the fill at a power density of at least about 50 watts/cc.
 10. Theapparatus of claim 2 wherein said bulb includes electrodes.
 11. A lampfor providing visible radiation, comprising,a light transmissiveenvelope, a fill enclosed in said envelope which includes elementalselenium when excited, which elemental selenium is present duringexcitation in an amount such that when said fill is excited bysufficient microwave or r.f. power, the excited fill emits radiationfrom the elemental selenium with substantially all of the radiation fromthe elemental selenium being emitted in a continuous band principallywithin the visible range and with most of the visible radiation emittedby the fill being provided by the elemental selenium, and means forexciting said fill with sufficient microwave or r.f. power so that saidelemental selenium emits said radiation substantially all of which is ina continuous band principally within the visible range.
 12. The lamp ofclaim 11 wherein said fill further includes a starting gas.
 13. A lampfor providing visible radiation, comprising,a light transmissiveenvelope, a fill enclosed in said envelope which includes elementalsulfur when excited, which elemental sulfur is present during excitationin an amount such that when said fill is excited by sufficient microwaveor r.f. power, the excited fill emits radiation from the elementalsulfur with substantially all of the radiation from the elemental sulfurbeing emitted in a continuous band principally within the visible rangeand with most of the visible radiation emitted by the fill beingprovided by the elemental sulfur, and means for exciting said fill withsufficient microwave or r.f. power so that said elemental sulfur emitssaid radiation substantially all of which is emitted in a continuousband principally within the visible range.
 14. A lamp bulb for providingvisible radiation, comprising,a light transmissive envelope, and a fillin the envelope which contains elemental selenium and elemental sulfurwhen excited, which are present in amounts during excitation such thatwhen the fill is excited with sufficient power, the excited fill emitsvisible radiation from the elemental selenium and from the elementalsulfur with substantially all of the radiation from each of theelemental sulfur and the elemental selenium being emitted in acontinuous band principally within the visible range.
 15. An apparatuscomprised of the lamp bulb of claim 14 in combination with;means forexciting said fill with sufficient power to cause said elementalselenium and said elemental sulfur to emit said radiation, substantiallyall of which is in a continuous band within the visible range.
 16. Theapparatus of claim 15 wherein the pressure of the fill at operating isat least about one atmosphere.